1. Field of the Invention
This invention relates to the preparation and use of a novel class of substantially monomeric aminoplasts as crosslinking agents. The crosslinkers are prepared from 2,4,6-triamino-1,3,5-triazine, hereinafter "melamine", and isopropenyl-alpha, alpha-dimethylbenzyl isocyanate, hereinafter "TMI", by a monoaddition reaction followed by methylolation and etherification.
2. Description of the Related Art
To effectively crosslink with a variety of widely available difunctional materials such as diols, dicarboxylic acids, dimercaptans, and diamides, a monomeric crosslinking agent is required to have a functionality effective for crosslinking of at least two. In many cases, however, even trifunctional aminoplast crosslinking agents do not give rise to sufficient crosslinking density in cured films or objects due to incomplete reaction of the functional groups, and as a result, cured films with inferior physical and resistance properties are obtained.
The problem of insufficient crosslinking density may be overcome by using a higher functional aminoplast crosslinker such as hexamethoxymethyl melamine. In these cases, however, the films obtained sometimes have low flexibility due to the somewhat rigid network produced in the films upon cure.
The above-identified problems of insufficient crosslinking of the low functionality crosslinkers and the low flexibility of the highly functional crosslinkers are both overcome by using typically tetrafunctional guanamine-derived aminoplast crosslinking agents. However, guanamine-derived crosslinkers are more difficult and more costly to prepare than melamine-derived crosslinkers. Furthermore, some guanamine crosslinkers such as N,N,N',N'-tetraalkoxymethylbenzoguanamines have insufficient resistance properties and have inferior stability towards the degradative action of ultraviolet light.
It is the object of this invention to obtain melamine-derived, substantially monomeric aminoplast crosslinking agents having olefinic functionality which are capable of producing, upon cure, films which have good acid resistance properties, environmental etch resistance, and a good balance of hardness and flexibility.